How to append text to the end of a Text datablock with Python
Write nothing first

Yes it writes at the cursor location, but will notice then seeks to file end. As mentioned in doc string

&gt;&gt;&gt; t = D.texts['Text']
&gt;&gt;&gt; t.write(
write()
Text.write(text)
write text at the cursor location and advance to the end of the text block


Simply write nothing to seek to EOF

t.write("")


Alternatively can set the cursor, as an example have used ints greater than existing lines and character length to make sure the cursor is at EOF. 

 t.cursor_set(44444444, character=44444444)


in both cases may require writing a new blank line.

t.write("\n")